Characterization of taxonomically restricted genes in a phylum-restricted cell type

Computational and functional genomic analyses in Hydra magnipapillata suggest that taxonomically-restricted genes are involved in the evolution of morphological novelties such as the cnidarian nematocyt

A Novel Gene Family Controls Species-Specific Morphological Traits in Hydra

Understanding the molecular events that underlie the evolution of morphological diversity is a major challenge in biology. Here, to identify genes whose expression correlates with species-specific morphologies, we compared transcriptomes of two closely related Hydra species. We find that species-specific differences in tentacle formation correlate with expression of a taxonomically restricted gene encoding a small secreted protein. We show that gain of function induces changes in morphology that mirror the phenotypic differences observed between species. These results suggest that “novel” genes may be involved in the generation of species-specific morphological traits

Genetic interference with HvNotch provides new insights into the role of the Notch-signalling pathway for developmental pattern formation in Hydra

Abstract The Notch-signalling pathway plays an important role in pattern formation in Hydra. Using pharmacological Notch inhibitors (DAPT and SAHM1), it has been demonstrated that HvNotch is required for head regeneration and tentacle patterning in Hydra. HvNotch is also involved in establishing the parent-bud boundary and instructing buds to develop feet and detach from the parent. To further investigate the functions of HvNotch, we successfully constructed NICD (HvNotch intracellular domain)-overexpressing and HvNotch-knockdown transgenic Hydra strains. NICD-overexpressing transgenic Hydra showed a pronounced inhibition on the expression of predicted HvNotch-target genes, suggesting a dominant negative effect of ectopic NICD. This resulted in a “Y-shaped” phenotype, which arises from the parent-bud boundary defect seen in polyps treated with DAPT. Additionally, “multiple heads”, “two-headed” and “ectopic tentacles” phenotypes were observed. The HvNotch-knockdown transgenic Hydra with reduced expression of HvNotch exhibited similar, but not identical phenotypes, with the addition of a “two feet” phenotype. Furthermore, we observed regeneration defects in both, overexpression and knockdown strains. We integrated these findings into a mathematical model based on long-range gradients of signalling molecules underlying sharply defined positions of HvNotch-signalling cells at the Hydra tentacle and bud boundaries

A novel gene family controls species-specific morphological traits in Hydra.

Understanding the molecular events that underlie the evolution of morphological diversity is a major challenge in biology. Here, to identify genes whose expression correlates with species-specific morphologies, we compared transcriptomes of two closely related Hydra species. We find that species-specific differences in tentacle formation correlate with expression of a taxonomically restricted gene encoding a small secreted protein. We show that gain of function induces changes in morphology that mirror the phenotypic differences observed between species. These results suggest that "novel" genes may be involved in the generation of species-specific morphological traits

Real time dynamics of β-catenin expression during hydra development, regeneration and wnt signalling activation

Understanding the dynamic cellular behaviours driving morphogenesis and regeneration is a long-standing challenge in biology. Live imaging, together with genetically encoded reporters, may provide the necessary tool to address this issue, permitting the in vivo monitoring of the spatial and temporal expression dynamics of a gene of interest during a variety of developmental processes. Canonical Wnt/β-catenin signalling controls a plethora of cellular activities during development, regeneration and adulthood throughout the animal kingdom. Several reporters have been produced in animal models to reveal sites of active Wnt signalling. In order to monitor in vivo Wnt/β-catenin signalling activity in the freshwater polyp Hydra vulgaris, we generated a β-cat-eGFP transgenic Hydra, in which eGFP is driven by the Hydra β-catenin promoter.We characterized the expression dynamics during budding, regeneration and chemical activation of the Wnt/β-cat signalling pathway using light sheet fluorescence microscopy. Live imaging of the β-cat-eGFP lines recapitulated the previously reported endogenous expression pattern of β-catenin and revealed the dynamic appearance of novel sites of Wnt/β-catenin signalling, that earlier evaded detection by mean of in situ hybridization. By combining the Wnt activity read-out efficiency of the β-catenin promoter with advanced imaging, we have created a novel model system to monitor in real time the activity of Hydra β-cat regulatory sequences in vivo, and open the path to reveal β-catenin modulation in many other physiological contexts